Methods and compositions for treating conditions mediated by oxidative stress or electrophilic environmental toxins

ABSTRACT

Methods and compositions are disclosed for treating a subject with a disease or tissue injury mediated by cellular oxidative stress or with an environmental toxicity due to an electrophilic toxicant or pollutant, and for providing a nutritional supplement to a subject and for providing a skin treatment for a subject, where the methods comprise administering to the subject a 1,3-dicarbonyl compound.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/397,213 filed on Jun. 8, 2010, the contents of which are herebyincorporated by reference.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under grant number RO1ES03830 21-24 awarded by the National Institute of Environmental HealthSciences. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Throughout this application various publications are referred to insuperscript. Full citations for these references may be found at the endof the specification. The disclosures of these publications are herebyincorporated by reference in their entirety into the subject applicationto more fully describe the art to which the subject invention pertains.

It is now recognized that many environmental toxicants (e.g., acrolein,chlorpyrifos methyl-mercury), as well as the endogenous mediators ofcellular oxidative stress (e.g., free radicals, metal ions, unsaturatedaldehydes), are electron deficient species (i.e., electrophiles).Substantial evidence indicates that these electrophilic toxicants causecell damage by reacting with nucleophilic targets on biologicalmacromolecules^(21, 37, 53, 55, 58, 59, 60, 62, 73, 83, 84). Thus, forexample, α,β-unsaturated carbonyl/aldehyde compounds (type-2 alkenes)are an important class of environmental pollutants that includesacrolein, acrylamide and methyl vinyl ketone. Humans are pervasivelyexposed to these chemicals through natural sources, diet, industrialpollution and occupation, and the toxicological consequences of suchexposures have been well documented^(14, 45, 58, 94). The commonα,β-unsaturated carbonyl/aldehyde structure of the type-2 alkenes is asoft electrophile, and current evidence suggests that these chemicalscause toxicity by forming 1,4-Michael adducts with the soft nucleophilicthiolate state of protein sulfhydrylgroups^(17, 22, 45, 56, 57, 61, 77.)

Electrophilic species also play a prominent role in cellular oxidativestress, which is defined as an imbalance between the production ofreactive oxygen species (ROS) and their removal via endogenousantioxidant systems. Oxidative stress is not only involved in the normalaging process, but is a pathogenic feature of many diseases (e.g.,atherosclerosis, diabetes, Alzheimer's disease) and tissue injury states(e.g., spinal cord trauma, stroke). It is initiated by univalentreduction of molecular oxygen to form the superoxide anion radical.Subsequent dismutation via superoxide dismutase (SOD) yields hydrogenperoxide, which is converted via the metal ion (Cu, Fe)-catalyzed Fentonreaction to the highly toxic hydroxyl radical. This electron-deficientspecies can damage cells by direct interactions with macromolecules(e.g., DNA/RNA base oxidation, oxidative protein damage) and throughmembrane lipid peroxidation. Peroxidative fragmentation ofpolyunsaturated fatty acids (e.g., arachidonic and linoleic acids)generates lipid hydroperoxides that can undergo chain cleavage to yieldtoxic α,β-unsaturated aldehyde derivatives such as acrolein and4-hydroxy-2-nonenal (HNE; reviewed in^(33, 42, 49, 59, 61, 81)). Theseendogenous derivatives are highly reactive electrophiles that readilyform adducts with nucleophilic sidechains on protein cysteines and otheramino acid residues (e.g., see^(56, 52, 62); reviewed in^(28, 77, 94)).Such protein adduct formation has been linked to broad cytotoxicconsequences including inhibition of enzyme activity, mitochondrialdysfunction and disruption of cell signaling pathways. Accordingly, the“aldehyde burden” imposed by lipid peroxidation is now thought to be acritical pathogenic component of cellular oxidativestress^(5, 39, 69, 95, 96, 97) (reviewed in^(18, 27, 58, 60).) Oxidativestress can, therefore, be viewed as the sequential generation ofelectrophiles that mediate cell injury and death. Thus, electrophilesare a large class of endogenous and exogenous toxicants that playsignificant roles in pathophysiological processes.

Pharmacological treatment (e.g., N-aceyl cysteine) of manyenvironmentally-derived toxicities (e.g., acrylamide contaminatedwell-water or industrial acrylonitrile poisoning) has often met withlimited success. Moreover, many of the current pharmacotherapeuticvenues (e.g., antioxidant therapy—α-tocopherol, β-carotene) availablefor treatment of certain disease states (e.g., Parkinson's disease) andtraumatic injuries (e.g., spinal cord injury) are either palliative orhave disappointing effectiveness. The complexity of the underlyingetiologies is the likely explanation for the limited performance ofthese therapies. The research community almost uniformly agrees that theeffective management of these pathogenic states will require either, atherapeutic “cocktail” involving several drugs or a multifunctionalcompound that can block the pathophysiological cascade at multiplerate-limiting steps. The present invention addresses the need forimproved methods and compositions for treating subjects with diseasesand tissue injury conditions that have cellular oxidative stress as amolecular etiology, such as atherosclerosis, diabetes, Alzheimer'sdisease, stroke and traumatic spinal cord injury, and for treatingsubjects with environmentally-derived toxicities.

SUMMARY OF THE INVENTION

The present invention provides methods of treating a subject with adisease or tissue injury mediated by cellular oxidative stress or asubject with an environmental toxicity due to an electrophilic toxicantor pollutant, the methods comprising administering to the subject atherapeutically effective amount of a compound of formula (I) asdescribed herein.

The invention also provides methods of providing a nutritionalsupplement to a subject comprising administering to the subject acompound of formula (I) as described herein.

The invention further provides methods of treating the skin of a subjectcomprising administering to the skin of the subject a compound offormula (I) as described herein.

The invention further provides compositions i) for treating a subjectwith a disease or tissue injury mediated by cellular oxidative stress,ii) for treating a subject with an environmental toxicity due to anelectrophilic toxicant or pollutant, iii) for treating a subject's skin,and iv) as nutritional supplements, the composition comprising acompound of formula (I) as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Structures of acetylacetone (AcAc), 1,1,1-trifluoropentanedione(TFPD), and 5,5-Dimethyl-1,3-cyclohexanedione (Dimedone).

FIG. 2A-2C. A) Curcumin is a hydrophobic multifunctional compound. Itconsists of a 1,3-dione system (circled “A”), two phenol portions(circled “B”) and two carbon-carbon double bonds (not circled), whichare conjugated with both the aromatic systems and the carbonylfunctions. Curcumin exists as an equilibrating pair of keto-enol isomers(shown in B), rather than the circled (“A”) diketo structure shown inA). The phenol groups of curcumin (circled “B”) have generatedsignificant attention based on their presumed role in antioxidantbehavior. However, recent evidence indicates that the antioxidantproperties of this phytopolyphenol are due to the effects of “A” and“B”. Thus, in ionizing solutions, deprotonation of enol (shown in C)yields the highly nucleophilic enolate carbanion, which can trapelectrophilic free radicals.

FIG. 3A-3B. A) Relative abilities of dicarbonyl analogues in vitro toslow N-acetyl cysteine (NAC) sulfhydryl loss induced by acroleinco-incubation. The slope of each regression line represents thepseudo-first order rate constant, which is presented parenthetically. B)shows the effect of elevated pH on sulfhydryl protection provided byAcAc or DEM.

FIG. 4. Effects of 1,3-dicarbonyl compounds and phloretin (PHL), aphytopolyphenol, on radiolabeled dopamine (DA) membrane transport incontrol striatal synaptosomes. Results demonstrate the weak toxicity ofthe 1,3-dicarbonyl analogs and the relatively significant in vitrotoxicity of phloretin.

FIG. 5A-5B. Effects of 1,3-dicarbonyl or phloretin (PHL) on theinhibition of radiolabeled dopamine (DA) transport (A) and loss of freesulfhydryl groups (B) in acrolein-exposed striatal synaptosomes.

FIG. 6. Effects of 1,3-dicarbonyl derivatives or phloretin (PHLOR) oncell viability in acrolein-exposed MN9D cultures. Data are expressed asmean percentage control, and calculated LC₅₀s for loss of cell viabilityare provided.

FIG. 7. Effects of 1,3-dicarbonyl on cell viability in H₂O₂-exposed MN9Dcultures (n=3-4 experiments). Data are expressed as mean percentagecontrol SEM, and calculated LC₅₀s for loss of cell viability areprovided.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provide a method of treating a subject with adisease or tissue injury mediated by cellular oxidative stress or asubject with an environmental toxicity due to an electrophilic toxicantor pollutant, the method comprising administering to the subject atherapeutically effective amount of a compound of formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof.

As used herein, to treat a subject with a disease or tissue injurymediated by cellular oxidative stress or a subject with an environmentaltoxicity due to an electrophilic toxicant or pollutant means toalleviate a sign or symptom associated with the disease, injury orenvironmental toxicity.

The disease or tissue injury can be, for example, atherosclerosis,diabetes, Alzheimer's disease, stroke or traumatic spinal cord injury.

The environmental electrophilic toxicant or pollutant can be, forexample, acrolein, acrylamide, methyl vinyl ketone, chlorpyrifosmethyl-mercury, an α,β-unsaturated aldehyde derivative, anα,β-unsaturated carbonyl derivative, a heavy metal, an organophosphateinsecticide, acrylamide contaminated well-water or an industrialacrylonitrile. For example, the subject can have mercury (Hg), lead (Pb)or arsenic (As) poisoning. An electrophile is attracted to electrons andparticipates in a chemical reaction by accepting an electron pair inorder to bond to a nucleophile. A nucleophile forms a chemical bond toits reaction partner (the electrophile) by donating both bondingelectrons.

The compounds can be used, for example, to prevent or reducehepatotoxicity.

The invention also provides a method of providing a nutritionalsupplement to a subject comprising administering to the subject acompound of formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof.

The invention further provides a method of treating the skin of asubject comprising administering to the skin of the subject a compoundof formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof.

The compound can be used, for example, to prevent or treat an agingeffect on the skin or to prevent or treat sun damage to the skin. Forexample, the compound can be used to treat or prevent wrinkles.

The invention further provides a composition i) for treating a subjectwith a disease or tissue injury mediated by cellular oxidative stress,ii) for treating a subject with an environmental toxicity due to anelectrophilic toxicant or pollutant, iii) for treating a subject's skin,or iv) for providing a nutritional supplement to a subject, thecomposition comprising a compound of formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof.

The compound used in the any of the methods disclosed herein or in anyof the compositions disclosed herein can have, for example, thestructure

or that of its enol tautomers

or any anionic species formed from either the dione or enols with thefollowing structure

In any of the compounds used in any of the methods disclosed herein orin any of the compositions disclosed herein, any ring formed between R₂with R₁ and/or R₃ can be independently a 4-12 member ring, for example,a 5-6 member ring. Furthermore, any ring formed between R₂ with R₁and/or R₃ can independently contain one or more O, S, N or substitutedN, where substitution at N is any alkyl or acyl group.

In any of the compounds used in any of the methods disclosed herein orin any of the compositions disclosed herein, any alkyl can beindependently C1-C6 alkyl, for example, C1-C3 alkyl.

The compound used in the any of the methods disclosed herein or in anyof the compositions disclosed herein can also have, for example, thestructure

wherein R₄=H, alkyl, alkoxy, acyloxy, aryl or acyloxyaryl; or a tautomerthereof.

More preferred compounds include

or a tautomer thereof.

Pharmaceutically acceptable salts that can be used include non-toxicsalts derived from inorganic or organic acids, including, for example,the following acid salts: acetate, adipate, alginate, aspartate,benzoate, benzenesulfonate, bisulfate, butyrate, citrate, camphorate,camphorsulfonate, cyclopentanepropionate, digluconate, dodecylsulfate,ethanesulfonate, formate, fumarate, glucoheptanoate, glycerophosphate,glycolate, hemisulfate, heptanoate, hexanoate, hydrochloride,hydrobromide, hydroiodide, 2-hydroxyethanesulfonate, lactate, maleate,malonate, methanesulfonate, 2-naphthalenesulfonate, nicotinate, nitrate,oxalate, palmoate, pectinate, persulfate, 3-phenylpropionate, phosphate,picrate, pivalate, propionate, p-toluenesulfonate, salicylate,succinate, sulfate, tartrate, thiocyanate, and undecanoate.

The compounds can be administered to the subject in a pharmaceuticalcomposition comprising a pharmaceutically acceptable carrier. Examplesof acceptable pharmaceutical carriers include, but are not limited to,additive solution-3 (AS-3), saline, phosphate buffered saline, Ringer'ssolution, lactated Ringer's solution, Locke-Ringer's solution, KrebsRinger's solution, Hartmann's balanced saline solution, and heparinizedsodium citrate acid dextrose solution. The pharmaceutically acceptablecarrier used can depend on the route of administration. Thepharmaceutical composition can be formulated for administration by anymethod known in the art, including but not limited to, oraladministration, parenteral administration, intravenous administration,transdermal administration, intranasal administration, andadministration through an osmotic mini-pump.

The compounds can be applied to the skin, for example, in compositionsformulated as skin creams, or as sustained release formulations orpatches.

The invention also provides for the use of a compound of formula (I) fortreating a subject with a disease or tissue injury mediated by cellularoxidative stress or with an environmental toxicity due to anelectrophilic toxicant or pollutant. The invention further provides forthe use of a compound of formula (I) as a nutritional supplement or fortreating the skin.

Compounds that can be used in the methods of the present invention canbe obtained commercially from, e.g., Sigma-Aldrich Inc., or preparedusing methods well known to those familiar with the art of organicsynthesis.

This invention will be better understood from the Experimental Details,which follow. However, one skilled in the art will readily appreciatethat the specific methods and results discussed are merely illustrativeof the invention as described more fully in the claims that followthereafter.

EXPERIMENTAL DETAILS Introduction

Enolates formed from 1,3-dicarbonyl compounds, such as acetylacetone(AcAc) and dimedone (DMD), are highly nucleophilic carbanions that canreadily react with or scavenge electrophiles (FIG. 1). Becauseelectrophiles (e.g., acrolein, metal cations, oxygen radicals) are keycomponents of many pathogenic scenarios (e.g., heavy metal poisoning,oxidative stress), it was hypothesized that AcAc and other1,3-dicarbonyls might provide significant cytoprotection through theirability to scavenge toxic electrophiles. Indeed, as demonstrated herein,a series of 1,3-dicarbonyl derivatives provided cytoprotection inseveral experimental models of electrophile toxicity (see below).Although the idea that 1,3-dicarbonyl compounds might be cytoprotectiveis unprecedented, it is based on the recognition that curcumin,phloretin and other plant-derived polyphenolic compounds(phytopolyphenols) also exhibit ionizable enol moieties that appear tobe responsible for their well-documented antioxidant andantiinflammatory properties (FIG. 2A). However, certain chemicalcharacteristics of these polyphenolic chemicals, which the non-phenolic1,3-dicarbonyls do not possess, could limit clinical utility, i.e.,chemical instability, toxicity and poor bioavailability. Thus,1,3-dicarbonyl enol compounds represent a rational basis for designingsafe, efficacious cytoprotectants with broad therapeutic applications.

Curcumin, Phloretin and Related Phytopolyphenols: Enolate-BasedCytoprotection.

There is abundant evidence that plant-derived polyphenolic compounds(phytopolyphenols) have cytoprotective properties with broad clinicalapplications. For example, curcumin (Curcuma longa Linn) is the activeingredient in numerous traditional medicines of China and India (FIG.2A)^(3, 35). Research has shown that curcumin has antioxidative,anti-inflammatory, chemopreventive and antitumor properties (reviewedin^(35, 67, 79)). Corresponding clinical trials have demonstrated thatthis phytopolyphenol is useful in treating numerous diseases; e.g.,Alzheimer's disease, epilepsy, cervical cancer and diabetes (reviewedin^(3, 35, 38)). Human consumption of other naturally occurringpolyphenols, such as the flavonoids (e.g., resveratrol in red wine,phloretin in apple skins and epigallocatechin gallate in green tea), hasbeen associated with a reduction in the incidence of cancer, stroke andcoronary heart disease (reviewed in^(6, 15, 44, 64, 99)). Basic researchhas shown that the flavonols, chalcones and other dietary flavonoidshave significant cytoprotective actions in various in vitro systems andanimal models (e.g., see^(19, 26, 36)). Until recently, it was assumedthat the protective effects of these compounds were related to theirantioxidant actions. However, evidence now indicates that cytoprotectionis more complex and involves not only free radical trapping, but alsometal ion chelation and scavenging of toxic aldehyde species; e.g.,acrolein and HNE (4-hydroxy-2-nonenal). The structural determinant ofthese cytoprotective effects is the enol moiety of the phytopolyphenolstructure. In this regard, the central heptadienone bridge of curcumin(circled A of FIG. 2A) is considered to be critical^(12, 89, 93). Thismoiety exists as equilibrating keto-enol isomers with the enol formpredominating in ionizing solutions such as biological buffers (FIG.2B). The enol of curcumin is a 1,3-dicarbonyl; i.e., two carbonyl groupsseparated by one (α) carbon. The hydrogens at the central α-carbon ofsuch enol compounds are acidic and, when removed, a carbanion is formedas the conjugate-base. The resulting anionic enolate, like most bases,is a site of nucleophilic reactivity (FIG. 2C). Similarly, flavonoidpolyphenols (e.g., phloretin) are characterized by multiple dicarbonylenol moieties (note: all phenols are enols). Phloretin, for example, hasat least three enolic sites that can potentially form a highlynucleophilic enolate anion (structures not shown).

Relation of Enolate Nucleophilicity to Phytopolyphenol Cytoprotection:

Electrophiles such as free radicals, metal ions and aldehyde by-productsare important pathogenic components of oxidative stress. Therefore,nucleophile-based scavenging of these toxic electrophiles hassubstantial cytoprotective potential. Evidence provided by Litwinienkoand Ingold⁵⁰ indicated that the nucleophilic enolate of curcumininitially reacts with free radicals to form a β-diketonyl radical. Thisis followed by proton donation from the phenol and, through a processknown as single proton loss electron transfer (SPLET), an electronmigrates through the delocalized system to restore the keto-enol groupand convert the phenolate to a phenoxyl radical. Flavonoid polyphenolsalso quench free radicals via a similar mechanism of enolate-trappingand proton donation^(70, 100). The nucleophilic enolate moiety ofcurcumin also functions as a bidentate chelator of iron [Fe(III)],copper [Cu(II)] and other electrophilic metal ions^(10, 43, 88). Thechelation chemistry of curcumin is based on the well-described processof Fe(III) chelation by the nucleophilic enolate of AcAc. Flavonoidsalso chelate metals through a curcumin-like mechanism^(64, 65, 70).Metal ion chelation presumably affords cytoprotection by limiting theparticipation of iron and copper in the Fenton reaction and therebyreducing subsequent generation of the highly toxic hydroxyl radical.Finally, several classes of flavonoids including the flavan-3-ols,theaflavins and dihydrochalcones were shown to form adducts withacrolein, HNE and other electrophilic α,β-unsaturated carbonyl/aldehydeproducts of lipid peroxidation^(13, 51, 72, 80, 85, 101, 102). Phloretinwas the most effective flavonoids tested and mass spectrometric analysesshowed that electrophile adduction was mediated through the C-3 enolsite^(85, 102). A growing body of evidence^(2, 40, 46, 78) also suggeststhat curcumin can scavenge acrolein and HNE through the enolate moiety.As will be discussed, the ability to adduct toxic aldehydes hassubstantial mechanistic relevance to cytoprotection. Thus, curcumin andthe flavonoid compounds have multiple cytoprotective actions likelylinked to the nucleophilicity of enolate moieties. The pleiotropiccharacter of phytopolyphenols has tremendous implications forefficacious cytoprotection, since the oxidative stress cascade could betruncated at numerous steps; i.e., the Fenton reaction, subsequent freeradical dissemination and toxic aldehyde generation.

Phytopolyphenol Disadvantages:

Despite numerous potentially beneficial actions, there are significantdisadvantages that might ultimately limit the clinical applications ofphytopolyphenols. Wang et al.⁹² reported that curcumin in phosphatebuffer (pH 7.2, 37C) was 90% decomposed within 30 minutes. Theseinvestigators identified a primary decomposition product,trans-6-(4′-hydroxy-3′-methoxyphenyl)-2,4-dioxo-5-hexenal, and severalminor products; e.g., vanillin, ferulic acid and feruloylmethane. Theobservation that these decomposition products (e.g., ferulic acid) werealso associated with in vivo administration suggested that curcumin isunstable in physiological solutions. There is also growing in vitroevidence that curcumin and certain flavonoids are cytotoxic, primarilythrough ROS-mediated cell damage; e.g.,see^(31, 32, 47, 71, 82, 87, 98). Perhaps more problematic, thephytopolyphenols exhibit limited bioavailability^(15, 75), which islikely related to the water insolubility of the polyphenolic structure.The limited bioavailability poses numerous pharmaceutical and formularyissues (e.g., large doses, lipidated formulations) that must beaddressed if the phytopolyphenols are to be used clinically.

1,3-Dicarbonyl Enols: A New Class of Cytoprotectants:

As discussed above, the cytoprotective properties of phytopolyphenolsappear to be related to the nucleophilic enolate of the correspondingenol moieties. The central heptadienone bridge of curcumin, which hasbeen identified as the seat of corresponding cytoprotective actions, isa 1,3-dicarbonyl enol (FIG. 2A). AcAc, MPD and structurally relatedderivatives are non-phenolic 1,3-dicarbonyl chemicals (FIG. 1). Likecurcumin, these chemicals exist as keto-enol tautomers with the enolisomer predominating in biological solutions. Ionization yields thehighly nucleophilic anionic enolate⁶³. The shared nucleophilic enolatemoiety suggests that the 1,3-dicarbonyl compounds exhibit acytoprotection profile similar to that of curcumin. Indeed, metal ionchelation is a well-documented trait of the 1,3-dicarbonylcompounds^(63, 87) and, although not as well studied, free radicaltrapping is a potential property⁵⁰. The 1,3-dicarbonyls also exhibit thephytopolyphenolic property of aldehyde adduction; i.e., AcAc and severalanalogs formed adducts with soft electrophilic chemicals (i.e.,benzhydrylium ions¹⁶). In several in vitro models of aldehyde (acrolein)toxicity, many of the same 1,3-dicarbonyl enols were highlycytoprotective through formation of 1,4-Michael adducts. Thispresumption has significant precedence since Michael addition, one ofthe most well known reactions in organic chemistry, was originallydefined by the conjugate addition of an enolate ion to an αβ-unsaturatedaldehyde derivative⁶³. Thus, the 1,3-dicarbonyls compounds and thedietary polyphenols can undergo common chemical reactions (i.e., metalchelation, free radical trapping and aldehyde adduction) that have broadcytoprotective implications. However, in contrast to thephytopolyphenols, the 1,3-dicarbonyls (FIG. 1) are simple, non-phenolicand can be relatively water-soluble compounds. Aqueous-solubilitysuggests that the bioavailability of these compounds is greater thanthat of curcumin and other dietary polyphenols. The 1,3-dicarbonylsenols are also chemically stable compounds with limited toxicity at thecellular (FIG. 4) and whole animal (AcAc LD₅₀=175 mg/kg) levels.Finally, quantum mechanical calculations (ω⁻, Table 1; see also¹¹)indicate that the nucleophilic reactivity of AcAc and related analogs issignificantly higher than that of the curcumin enolate. This suggeststhat the cytoprotective efficacy of the 1,3-dicarbonyl compounds couldbe substantial.

Example I Chemistry of the 1,3-Dicarbonyl Protectants and CytoprotectionStudies Chemistry of the 1,3-Dicarbonyl Protectants

The invention relates to the therapeutic and medicinal use of compoundswith the general formula (I):

Quantum Mechanical Calculations of Enolate Nucleophilicity:

The Hard and Soft, Acids and Bases (HSAB) theory of Pearson^(58, 62, 76)is a predictive chemical model based on the premise that softelectrophiles preferentially react with soft nucleophiles and hardelectrophiles react with hard nucleophiles. This is a quantifiableconcept where the designation of “hard” or “soft” is based oncorresponding inherent electronic characteristics that can be computedfrom the energies of the respective frontier molecular orbitals; i.e.,the Highest Occupied Molecular Orbital (E_(HOMO)) for the nucleophile orthe Lowest Unoccupied Molecular Orbital (E_(LUMO)) for the electrophile.These energies have been used to develop valid quantum mechanicalparameters that define the electrophilicity (ω) and nucleophilicity(ω⁻)⁴¹ of chemical species. Application of these parameters hassignificantly increased understanding of electrophile and nucleophilebehavior in various biological systems^(56, 57, 61, 68). Accordingly,the ω⁻ algorithm was used to calculate the relative nucleophilicities ofseveral 1,3-dicarbonyl compounds and curcumin using acrolein as theelectrophilic target (Table 1). Computations of nucleophilicity includedthe keto and enol isomers and the anionic enolate. Because the ω⁻ valuesfor the enol and keto isomers of all chemicals considered weresubstantially lower (100 fold) than the respective enolate values (datanot shown), it can be concluded that the enolate form is the relevantnucleophile; i.e., acrolein reacts the enolate, rather than with theenol or keto isomers. When other electrophile targets were applied(e.g., methylvinyl ketone, benzhydrylium ions) in the ω⁻ algorithm, thesame enolate reactivity was evident (data not shown). Finally, it isnoteworthy that the curcumin enolate is significantly less nucleophilicthan the enolate forms of the 1,3-dicarbonyl compounds (Table 1).

TABLE 1 Nucleophilicities and kinetic data for 1,3-dicarbonyl enolcompounds. Enolate ω⁻ pKa DEM 0.228 12.9 MPD 0.230 10.8 ACP 0.401 7.8DMD 0.174 5.3 AcAc 0.169 9.0 Meld. Acid 0.166 4.8 TFPD 0.099 4.7phloretin 0.105 7.3 curcumin 0.062 8.0The E_(LUMO) and E_(HOMO) energies were calculated using Spartan08(version 1.0.3) software (Wavefunction Inc., Irvine Calif.). Thenucleophilicity index (ω⁻) was calculated asω⁻=η_(A)(μ_(A)−μ_(B))²/2(η_(A)−η_(B))², where A=the selected enol andB=acrolein. Global (whole molecule) softness (σ) was calculated as theinverse of hardness or σ=1/η, where hardness (η)=(E_(LUMO)−E_(HOMO))/2and μ=(E_(LUMO)+E_(HOMO))/2. All values are presented as electron volts(see LoPachin et al.^(56, 57) for details). Abbreviations: DEM=diethylmalonate; MPD=3-methyl-2,4-pentanedione; ACP=2-acetylcyclopentanone;DMD=dimedone; AcAc=acetylacetone; Meldrum'sacid=2,2-dimethyl-1,3-dioxane-4,6-dione;TFPD=1,1,1,-trifluoro-2,4-pentanedione.

Cytoprotection Studies:

The idea that 1,3-dicarbonyl compounds are cytoprotective was completelyunexplored and, therefore, a series of studies was conducted todetermine respective in vitro cytoprotective capacities. To determinethe predictive value of ω⁻ calculations, respective nucleophilicities(Table 1) were calculated for the 1,3-dicarbonyl enol compounds and werecompared to the corresponding kinetic data. Kinetic assays show that therate of sulfhydryl loss associated with acrolein incubation was slowedpredictably by a structural series of enols. Furthermore, this kineticorder predicted the relative abilities of enol analogs to preventacrolein-induced toxicity in complex biological models, i.e., isolatedstriatal synaptosomes (nerve endings) and a cultured nerve cell line.

1,3-Dicarbonyl Protection of Sulfhydryl Groups: Kinetic Analyses andSynaptosome Model:

As an index of cytoprotection, these studies focused on the abilities of1,3-dicarbonyl compounds to prevent electrophile-induced loss of proteinand non-protein sulfhydryl groups. This experimental focus is based onsubstantial evidence that soft electrophiles, like acrolein, producetoxicity by forming Michael-type adducts with soft nucleophilic thiolate(anionic sulfhydryl) groups on functionally criticalproteins^(9, 17, 22, 56, 57) (reviewed in^(28, 58, 62, 77, 94)). If thenucleophilic enolates of 1,3-dicarbonyl derivatives are cytoprotectivethrough scavenging electrophiles, then these enols should be capable ofslowing the adduct reaction between an electrophile and a correspondingnucleophilic target. To test this hypothesis, a determination was madeof the ability of AcAc and other structurally related enol analogs toprevent sulfhydryl (nucleophile) adduction by acrolein (electrophile)⁵⁶.In this study, N-acetyl cysteine (NAC) was used as a sulfhydryl sourceand was incubated with both acrolein (150 μM) and a selected testcompound (50 μM) in Krebs buffer (pH 7.4, 30° C.). Free sulfhydrylconcentrations were determined over time (up to 15 mins) by the DTNBmethod of LoPachin et al.⁵². The adduct reaction between acrolein andNAC (FIG. 3A) followed pseudo-first order kinetics^(56, 57) as indicatedby the linear relationship (r² range=0.82-0.99) between log [SH/SH_(O)]versus time (where SH=sulfhydryl concentration at time t andSH_(O)=initial concentration at t_(O)). Results indicate that the1,3-dicarbonyl derivatives acted as surrogate nucleophilic targets andthereby slowed the loss of NAC sulfhydryl groups due to acroleinadduction (FIG. 3A). Specifically, acrolein alone caused a rapidreduction (mean rate±SE) in sulfhydryl concentration (rate=−78.4±7 nmolSH sec⁻¹). However, when acrolein was co-incubated with DMD orphloretin, the rate of sulfhydryl loss was substantially curtailed(−2.4±0.3 and −1.9±0.7 nmol SH sec⁻¹, respectively). AcAc (−24.9±5 nmolSH sec⁻¹) was somewhat less protective, whereas TFPD afforded modest,roughly equivalent, reductions in thiol loss (−52.1±5 nmol SH sec⁻¹).MPD was minimally protective (FIG. 3A), whereas DEM and 2,5-hexanedione(HD), a γ-diketone (i.e., carbonyl functions separated by two carbonatoms), were not effective at slowing the rate of thiol loss (FIG. 3A).To demonstrate that the formation of the enolate was dependent upon enolionization, the thiol protection afforded by DEM, AcAc and TFPD wasdetermined at pH 9.0 (FIG. 3B). AcAc (pKa 9.0—Table 1) at pH 9.0 wascompletely protective, whereas the ability of DEM (pKa 12.9—Table 1) toslow acrolein-induced thiol loss was significantly increased. ThispH-dependent effects reflects the increased enolate concentration at pH9.0, which is closer to the pKa of AcAc and DEM. In contrast, theprotective capacity of TFPD did not increase at the more basic pH (datanot shown), since at neutral pH this 1,3-dicarbonyl analog is mostly(99%) in the enolate-state (pKa 4.7—Table 1).

Because acrolein and other electrophilic α,β-unsaturated carbonylderivatives produce toxicity through preferential adduction of proteinsulfhydryl groups, the preservation of thiols in the preceding kineticstudies (FIG. 3) suggests that the 1,3-dicarbonyl derivatives haveprotective actions. Therefore, as an investigation of possiblecytoprotection, a determination was made of the relative abilities ofthe above 1,3-dicarbonyl structural series to prevent thiol loss inacrolein-exposed rat striatal synaptosomes (isolated CNS nerveterminals). Synaptosomes were prepared according to the methods ofLoPachin et al.⁵² and were exposed (Krebs buffer, pH 7.4, 30° C.×15mins) to graded concentrations of acrolein (1-1000 μM) alone or incombination with a 1,3-dicarbonyl derivative or control compound (500μM). The 1,3-dicarbonyl concentration was selected based on initialconcentration-response determinations, which showed that 500 μM providedthiol protection against an acrolein concentration that caused a 50%loss of sulfhydryl groups (IC₅₀; data not shown). Synaptosomalsulfhydryl content was determined by a DTNB method (see above) and datawere fitted by nonlinear regression analysis (r² for all curves ≧0.90).The respective IC₅₀s and 95% confidence intervals were calculated by theCheng-Prusoff equation (Prism 3.0, GraphPad Software). The selected1,3-dicarbonyls are carbanion nucleophiles and, therefore, the analysesalso included NAC as a representative thiolate-type nucleophile. Studieswere conducted to assess the in vitro toxicity of the selected enolderivatives (FIG. 4). Based on the respective IC₅₀s, the 1,3-dicarbonylcompounds are relatively weak toxicants (i.e., mM IC₅₀s), whereas thephytopolyphenol, phloretin, exhibits significant synaptosomal toxicity(i.e., μM IC₅₀s). As shown in FIG. 5A, the enols shifted theconcentration-response curve to the right for acrolein-inducedinhibition of DA transport, which resulted in corresponding increases inthe acrolein IC₅₀. Thus, DMD, Meldrum's acid, AcAc and NAC produced thelargest increases in the acrolein IC₅₀, whereas the changes induced byTFPD were more modest (FIG. 5A). Neither DEM nor HD significantlyaffected the acrolein IC₅₀. The rank order of synaptosomal function(FIG. 5A) and thiol (FIG. 5B) protection by the enol analogs wasequivalent to that defined in the preceding kinetic studies (FIG. 3A).This rank order reflects both the respective pKa values of the1,3-dicarbonyl derivatives and corresponding nucleophilicities (Table1). Specifically, DMD, with a pKa value of 5.3, will exist primarily(99%) as the acrolein-scavenging anionic enolate at pH 7.4. Based on thesignificant nucleophilicity of this analog (ω⁻=0.174), it is notsurprising that DMD is a powerful cytoprotectant. DEM is a betternucleophile (ω⁻=0.228) than DMD; however, it is not cytoprotective sincevery little enolate (<0.1%) is available at neutral pH given a pKa of12.9. Although TFPD is a weaker nucleophile (ω⁻=0.099) than the otherenol analogs (Table 1), this derivative offers some thiol protection atpH 7.4 through mass action of the more abundant enolate form (pKa=4.7).

1,3-Dicarbonyl Protection of Sulfhydryl Groups: Nerve Cell CultureModels:

The demonstrated ability of the 1,3-dicarbonyl analogs to preventacrolein-induced thiol loss suggests that the nucleophilic enolate ofthese chemicals could provide significant cytoprotection by scavengingelectrophilic mediators (e.g., free radicals, toxic aldehydes and metalions) of oxidative stress. As a more complex biological model, adetermination was made of the relative abilities of the 1,3-dicarbonylsto protect MN9D cells, a dopaminergic cell line, from acrolein- (FIG. 6)or hydrogen peroxide (H₂O₂)-induced cell death (FIG. 7). Briefly, twodays after plating, cells were incubated with AcAc (750 μM) for one hrfollowed by exposure to graded concentrations of either acrolein(0.50-150 μM×24 hrs) or H₂O₂ (50-750 μM×24 hrs). Cell viability wasdetermined by trypan blue (0.1%) exclusion. Living cells were counted ina hemocytometer and total cells per dish were calculated. Range-findingstudies showed that AcAc (50-1000 μM) provided concentration-dependentprotection against both acrolein- and H₂O₂-induced toxicity. Exposure ofcells to graded concentrations of acrolein (50-150 μM) caused cell deathwith an LC₅₀ of 96 μM (LC₅₀=acrolein concentration producing 50% celllethality; FIG. 6). Pre-incubation with AcAc or TFPD caused rightwardshifts in the respective acrolein curves and nearly 7-fold increases inthe LC₅₀ (641 μM or 582 μM; FIG. 6). As expected, neither DEM nor HDwere effective (FIG. 6). NAC provided nearly complete protection againstacrolein cytotoxicity, whereas phloretin (PHLOR; 100 μM) alone causedsubstantial cell loss (˜50%) and did not protect MN9D cell fromacrolein.

The relative abilities of the 1,3-dicarbonyl compounds to protect cellsagainst H₂O₂ toxicity was also determined (FIG. 7). This systemrepresents a more complete model of oxidative stress since the hydroxylradical formed from intracellular H₂O₂ during the Fenton reaction,subsequently mediates the generation of toxic aldehyde by-products suchas acrolein and 4-hydroxy-2-nonenal (HNE). The data show that AcAc andTFPD provide 3-fold protection against H₂O₂-induced cytotoxicity. Incontrast, NAC was significantly less efficacious and both DEM and HDwere ineffective.

CONCLUSIONS

Depending upon the respective pKa and nucleophilicity values, DMD, AcAcand other 1,3-dicarbonyl analogs provide substantial cytoprotection inseveral models of electrophile toxicity. Unlike conventionalantioxidants such as alpha-tocopherol and beta-carotene that trap freeradicals, the dicarbonyls have a broad profile of electrophilescavenging; e.g., hydroxyl radicals, metal ions and toxic unsaturatedaldehydes. In contrast, to the phytopolyphenols (phloretin, curcumin,resveratrol), the 1,3-dicarbonyls are water-soluble, chemically stableand non-toxic. The possibility that these chemicals have significantcytoprotective properties has not been considered previously. Thesecompounds, therefore, are outstanding candidates for pharmacotherapeuticapproaches to diseases and tissue injury conditions that have cellularoxidative stress as a molecular etiology.

These highly nucleophilic (electron-rich) compounds are potentiallyuseful in the prevention and treatment of broad pathogenic states, theetiologies of which involve electrophile (electron-deficient)-inducedcell damage (cytotoxicity). These electrophiles cause cell injury anddeath by reacting with and thereby disabling functionally criticalnucleophilic sites on biological macromolecules such as proteins andDNA. The cytotoxic electrophiles include environmental contaminants(e.g., acrolein, heavy metals, organophosphate insecticides) andendogenous mediators of cellular oxidative stress (e.g., oxygenradicals, metal cations and unsaturated aldehydes). The presentinvention provides a surrogate nucleophilic target for electrophiles andthereby protects cells from toxicity. The invention has substantialtherapeutic application given the ubiquitous presence of electrophilictoxicants in the environment and the almost generic involvement ofoxidative stress in many disease processes and tissue injury conditions;e.g., atherosclerosis, diabetes, Alzheimer's disease, stroke andtraumatic spinal cord injury. Pleitropic compounds can intercept thetoxic actions of electrophiles (i.e., free oxygen radicals, metalcations, unsaturated aldehydes) at multiple sites along the oxidativestress cascade. Thus, the invention is envisioned to be useful intreating chemical intoxication, since the majority of environmentaltoxicants are electrophiles. Therefore, these compounds and structurallyrelated analogs could be highly efficacious pharmacotherapeutic agentsthat have broad applications.

Example II In Vitro Studies with 2-Acetylcyclopentanone (2-ACP)

In vitro studies were conducted with 2-acetylcyclopentanone (2-ACP):

Relative to phytopolyphenols such as curcumin and resveratrol, 2-ACP isnon-toxic and water soluble. As such, this 1,3-dicarbonyl derivative hassubstantial bioavailability and, should, therefore provide in vivocytoprotection at relatively low doses (see Example III). Furthermore,the corresponding nucleophilic index (ω⁻) is relatively high (0.401 ev)(cf. Table 1) and the pKa (7.8) is close to physiological pH (7.4). Thismeans that the anionic enolate of 2-ACP is highly nucleophilic(reflected by the ω⁻ value) and that at cellular pH, nearly 50% of 2-ACPwill be in enolate state. This is in contrast to other putativeprotectants that have lower enolate nucleophilicity (e.g., curcumin)and/or higher pKa values (e.g., DEM).

Result are summarized below and described more fully in LoPachin et al.2011,¹⁰³ the contents of which are herein incorporated by reference.

Chemicals and Reagents:

Reagents were HPLC grade, and water was double-distilled and de-ionized,unless otherwise indicated. 3H-Dopamine (specific activity 23.5 Ci/mmol)was obtained from American Radiolabeled Chemicals (St. Louis, Mo., USA).Whatman GF/F filter paper was purchased from the Brandel Company(Gaithersburg, Md., USA). MN9D cells were a gift from Lisa Won, Ph.D.,University of Chicago. All other reagents were purchased from theSigma/Aldrich Chemical Company (Bellefonte, Pa., USA). b-Dicarbonylenols and other test compounds were dissolved in DMSO and were dilutedin buffer to final concentrations of ≦0.05% DMSO. Studies showed thatthis DMSO concentration did not affect 3H-DA uptake or cell viability.

1,3-Dicarbonyl Protection Against Acrolein-Induced Synaptosomal ThiolLoss and Dysfunctional³H-Dopamine (DA) Transport:

Studies were carried out using isolated brain nerve terminals (striatalsynaptosomes) exposed to acrolein as a model of electrophile-inducedtoxicity, as illustrated in FIG. 5A-5B. Acrolein is a soft electrophilethat inhibits protein function by forming adducts with soft nucleophiliccysteine residues and thereby causes synaptosomal toxicity. The abilitywas assessed of 2-ACP and other related 1,3-dicarbonyl analogs (500 μM)to prevent acrolein-induced inhibition of ³H-dopamine (DA) transport andthiol loss. Acrolein (0.001-1 mM) produced concentration-dependent lossof synaptosomal sulfhydryl groups (IC₅₀=74 μM), which was associatedwith parallel decreases in membrane ³H-DA transport (IC₅₀=66 μM).Co-incubation with 2-ACP provided substantial protection as evidenced bya rightward shift in the acrolein response curves and a 15-foldincreases in the corresponding IC₅₀ values for both thiol preservation(1109 μM) and inhibition of ³H-DA transport (IC₅₀=947 μM). Thisindicates that 2-ACP was significantly more protective than other1,3-dicarbonyl analogs or the phytopolyphenols tested; e.g., bycomparison of the respective IC₅₀ values for 2-ACP vs., e.g., Meldrum'sacid (MA) or acetylacetone (AcAc).

1,3-Dicarbonyl Protection of a Neuronal Cell Line: Acrolein and HydrogenPeroxide Toxicities:

Pre-incubation of MN9D cell cultures for 60 minutes with 2-ACP,1,3-cyclopentanedione (CPD) or N-acetyl cysteine (NAC) (750 μM each)completely prevented cell death induced by subsequent exposure to gradedconcentrations of acrolein (25-200 μM) (cf. FIGS. 6 and 7). AcAc and1,1,1-trifluoro-2,4-pentanedione (TFPD) significantly increased theacrolein LC₅₀ (96 μM), whereas 2,5-hexanedione (HD) a γ-diketone analog,produced a slight increase in LC₅₀. Dimedone (DMD) and MA did notprovide protection in acrolein-exposed MN9D cell cultures. However, thislack of cytoprotection was related to serum protein binding, sincestudies in serum-free medium demonstrated that both 1,3-dicarbonylderivatives produced substantial increases in the acrolein LC₅₀. Studiesof individual 1,3-dicarbonyls showed that graded concentrations of 2-ACP(100-750 μM) or AcAc (250-1000 μM) produced significant increases in theLC₅₀ reflected by progressive rightward shifts in the acrolein-inducedcell death curve. Thus, the rank-order of protection fromacrolein-induced toxicity in MN9D cultures mirrors that demonstrated inacrolein-exposed synaptosomes (i.e., 2-ACP≈NAC, CPD>AcAc, TFPD>>HD).Studies indicated that, although the β-dicarbonyl compounds did notcause toxicity, phloretin was a significant cytotoxicant exhibiting anLC₅₀ of 362 μM. Phloretin (100 μM) caused significant MN9D cell death(42%) and did not provide cytoprotection in acrolein-exposed cultures.

As a more direct model of oxidative stress, MN9D cell cultures wereexposed to graded H₂O₂ concentrations (200-800 μM; LC₅₀=254 μM) and therelative abilities of dicarbonyl and polyphenolic analogs to preventcell death were determined 2-ACP provided nearly complete protection inthis injury model, whereas AcAc and TFPD were modestly effective (750μM). Graded concentrations of 2-ACP (250-750 μM) or AcAc (500-1500 μM)produced significant increases in the LC₅₀ of H₂O₂ reflected byprogressive rightward shifts in the concentration-toxicity curves. NACwas less protective and both CPD and HD were ineffective. Phloretin (100μM) did not provide protection and instead potentiated H₂O₂ toxicity.Together, the results indicate that the rank-order of β-dicarbonylprotection in H₂O₂-exposed MN9D cell cultures was similar to those ofthe acrolein models; i.e., 2-ACP>AcAc, TFPD>>HD. However, there werenotable exceptions: although both NAC and CPD provided protectionagainst acrolein-induced toxicity in the synaptosomal and cell culturemodels, they failed to protect MN9D cells against peroxide-induced celldeath.

Free Radical Scavenging:

The relative abilities of selected 1,3-dicarbonyl compounds to scavengefree radicals were determined using the spectrophotometric method of Akand Gulcin (2008)⁴ that measures changes in the absorbance of the2,2-diphenyl-1-picrylhydrazyl radical. Consistent with previous studies,2,2-diphenyl-1-picrylhydrazyl radical (DPPH.) scavenging by curcumin wassubstantially faster than any compound tested. The thiol nucleophile,N-acetyl cysteine (NAC), exhibited modest free radical scavenging,whereas phloretin and the 1,3-dicarbonyl compounds were relatively weakDPPH.scavengers; e.g., 2-ACP was approximately 30-40 fold slower thancurcumin.

Metal Chelation:

The chelation of ferrous ion by a selected 1,3-dicarbonyl or otherexperimental compound was estimated by the method of Dairam et al.(2008).¹⁰⁴ Based on the concentration at which 50% Fe²⁺ chelationoccurs, EDTA (31 μM) and the 1,3-dicarbonyl, 2-ACP (211 μM) were themost potent chelating agents tested. AcAc was weaker (909 μM), whereasthe other 1,3-dicarbonyl congeners tested, phloretin and NAC exhibitedlittle, if any, Fe²⁺ chelating activity. Consistent with previousstudies, curcumin chelation of Fe²⁺ paralleled that of 2-ACP up to 100μM. Higher curcumin concentrations were not tested due to itsinsolubility in aqueous solutions.

Acrolein-Induced Thiol Loss:

The formation of Michael adducts with acrolein and other α,β-unsaturatedaldehydes has long been considered a characteristic reaction of1,3-dicarbonyl compounds, and it has recently been demonstrated thatphloretin also forms this type of adduct with acrolein. Therefore, as akinetic index of competitive thiol protection by enolate sequestration,the relative in vitro abilities of 1,3-dicarbonyl compounds andphloretin to slow the rate of acrolein-induced sulfhydryl loss weremeasured. Acrolein caused a rapid reduction (mean rate±95% confidenceinterval) in sulfhydryl (NAC) concentration; i.e., rate=−78.4±6.2 nmols⁻¹. When acrolein was pre-incubated with 2-ACP followed by the additionof NAC one hour later, corresponding sulfhydryl groups were completelypreserved. MA, DMD and phloretin provided significant thiol protection,whereas AcAc, CPD and TFPD were modestly effective. HD did not affectthe rate of acrolein-induced thiol loss. When acrolein was co-incubatedwith the test compounds (i.e., all chemicals added simultaneously),2-ACP again provided complete sulfhydryl protection, whereas phloretin,and the other 1,3-dicarbonyls were only marginally protective. Therespective differences in protection afforded by the pre- andco-incubation conditions reflects the relative rates of reaction betweenacrolein and the selected 1,3-dicarbonyl analogs. Thus, 2-ACP providedcomplete sulfhydryl protection regardless of the incubation scenario,indicating a relatively rapid rate of acrolein interaction. In contrast,thiol protection by the other congeners required pre-incubation withacrolein indicating a significantly slower reaction rate.

To demonstrate the role that acid strength (pK_(a)) plays in thesulfhydryl protection afforded by the β-dicarbonyls, kinetic studies ofthiol protection were conducted at pH 9.0. Results showed thatincreasing the pH substantially elevated the sulfhydryl preservation ofAcAc and diethylmalonate (DEM). With pKa values of 8.9 and 12.9respectively, the enolate concentrations of DEM and AcAc at pH 9.0 areincreased almost 100 fold (relative to those at pH 7.4) and, as would beexpected, parallel increases in sulfhydryl protection were observed;i.e., DEM slowed acrolein-induced thiol loss from −78.7±6.2 nmol s⁻¹ to−59.7±5.1 nmol s⁻¹ and AcAc slowed the rate of loss from −24.9±3.6 nmols⁻¹ to −2.43±2.2 nmol s⁻¹. TFPD (pKa=4.2) is completely ionized (>99%)at pH 7.4 and an increase in pH will not significantly alter thecorresponding enolate concentration. Hence, no increase in sulfhydrylprotection was expected for TFPD and none was observed at the higher pH.

Example III In Vitro Studies with 2-Acetylcyclopentanone (2-ACP)

This study was carried out in accordance with the NIH Guide for Care andUse of Laboratory Animals and approved by the Montefiore Medical CenterAnimal Care and Use Committee. Adult male rats (Sprague-Dawley, TaconicFarms, Germantown, N.Y., USA) were used in this study. Rats were housedindividually in polycarbonate boxes, and drinking water and PurinaRodent Laboratory Chow (Purina Mills, Inc., St. Louis, Mo., USA) wereavailable ad libitum.

2-ACP Toxicity in Rats and Protection from Hepatotoxicity Induced byCarbon Tetrachloride:

Male rats (200-250 gm) were injected (i.p.) with 2-ACP at threedifferent daily dose-rates: 100, 200 or 300 mg/kg/d×14 days. Rats wereobserved 3 times per week for signs of developing toxicity; i.e., bodyweight loss, general appearance, water/food consumption, gaitperformance and home cage behavior. Regardless of dose-rate, 2-ACP didnot cause overt signs of toxicity. As a model of in vivo oxidativestress, rats (200-250 gm) were administered 30 μl of carbontetrachloride (CCl₄) in corn oil (ip) following six daily doses of 2-ACP(200 mg/kg/d) by gavage. Twenty-four hours after CCl₄ intoxication,plasma biomarkers of hepatotoxicity, alanine transferase (ALT) andaspartate transferase (AST) were determined Results indicate that 2-ACPpretreatment of CCl₄-intoxicated rats significantly reduced theappearance of ALT by 40% and AST by 52% in plasma relative to ratstreated with toxicant only. These findings indicate that 2-ACP decreasedthe degree of hepatic cell death caused by CCl₄.

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1. A method of treating a subject with a disease or tissue injurymediated by cellular oxidative stress or a subject with an environmentaltoxicity due to an electrophilic toxicant or pollutant, the methodcomprising administering to the subject a therapeutically effectiveamount of a compound of formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof.
 2. A method of providing a nutritional supplement to a subjectcomprising administering to the subject a compound of formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof.
 3. A method of treating the skin of a subject comprisingadministering to the skin of the subject a compound of formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof.
 4. The method of claim 1, wherein the compound has thestructure


5. The method of claim 1, wherein any ring formed between R₂ with R₁and/or R₃ is independently a 4-12 member ring.
 6. The method of claim 5,wherein any ring formed between R₂ with R₁ and/or R₃ is independently a5-6 member ring.
 7. The method of claim 1, wherein any ring formedbetween R₂ with R₁ and/or R₃ independently contains one or more O, S, Nor substituted N, where substitution at N is an alkyl or acyl group. 8.The method of claim 1, wherein any alkyl is independently C1-C6 alkyl.9. The method of claim 8, wherein any alkyl is independently C1-C3alkyl.
 10. The method of claim 1, wherein the compound has the structure

wherein R₄=H, alkyl, alkoxy, acyloxy, aryl or acyloxyaryl; or a tautomerthereof.
 11. The method of claim 1, wherein the compound has thestructure


12. The method of claim 1, wherein the subject has a disease or tissueinjury mediated by cellular oxidative stress.
 13. The method of claim12, wherein the disease or tissue injury is atherosclerosis, diabetes,Alzheimer's disease, stroke or traumatic spinal cord injury.
 14. Themethod of claim 1, wherein the subject has an environmental toxicity dueto an electrophilic toxicant or pollutant.
 15. The method of claim 14,wherein the toxicant or pollutant is acrolein, acrylamide, methyl vinylketone, chlorpyrifos methyl-mercury, an α,β-unsaturated aldehydederivative, an α,β-unsaturated carbonyl derivative, a heavy metal, anorganophosphate insecticide, acrylamide contaminated well-water or anindustrial acrylonitrile.
 16. The method of claim 14, wherein thesubject has Hg, Pb or As poisoning.
 17. The method of claim 1, whereinthe compound prevents or reduces hepatotoxicity.
 18. The method of claim3, wherein the compound is used to prevent or treat an aging effect onthe skin or to prevent or treat sun damage to the skin.
 19. The methodof claim 18, wherein the compound is used to treat or prevent wrinkles.20. A composition for i) treating a subject with a disease or tissueinjury mediated by cellular oxidative stress, ii) treating a subjectwith an environmental toxicity due to an electrophilic toxicant orpollutant, iii) treating a subject's skin, or iv) providing anutritional supplement to a subject, the composition comprising acompound of formula (I)

wherein R₁ and R₂ are independently H, alkyl, alkoxy alkyl, acyloxyalkyl, aryl, aryloxy, acyloxy aryl, heteroaryl, heteroaryloxy, oracyloxy heteroaryl; X is COR₃, CO₂R₃, NO₂, CN, CON(R₃)₂, or SO₂R₃; R₃ isH, alkyl, alkoxy alkyl, acyloxy alkyl, aryl, aryloxy, acyloxy aryl,heteroaryl, heteroaryloxy, acyloxy heteroaryl, or trifluoromethyl;and/or R₂ forms a ring together with either R₁ or R₃, or R₂ forms ringswith both R₁ and R₃; wherein any ring formed between R₂ with R₁ and/orR₃ optionally and independently contains one or more O, S, N orsubstituted N, where substitution at N is an alkyl or acyl group;wherein any alkyl can independently be branched or unbranched; whereinany aryl or heteroaryl can independently be optionally substituted with—CH3, —NH2, —OH, ═O, halogen, alkyl, alkoxy, acyloxy, aryl and/oracyloxyaryl; or a tautomer thereof; or a geometric or optical isomerthereof; or racemate thereof; or a pharmaceutically acceptable saltthereof. 21-36. (canceled)